Project summary Breast cancer frequently metastasizes to be where it leads to osteolysis and poor clinical prognosis;however, the role of hydroxyapatite nanocrystals (HA, the mineral component of bone) in this process remains unclear due, in part, to the lack of appropriate culture models. The overall goal of these studies is to design a mineralized 3-D tumor model that captures the intrinsic 3-D cell-microenvironment interactions within bone- metastatic niches and nanostructural alterations of HA that may occur due to disease and aging. Specifically, we will develop porous poly (lactide-co-glycolide) (PLG) scaffolds that incorporate HA nanoparticles of defined physicochemical characteristics and assess the applicability and relevance of this 3-D tumor model to test the functional relationships between HA and osteolytic bone metastasis. This work will be accomplished in three specific aims: In Aim 1, we will develop the 3-D matrices by synthesizing monodispersed nanoparticles of HA with controlled/variable aspect ratios, crystallinities, and lattice substitutions and incorporating them into porous PLG scaffolds. In Aim 2, we will utilize these scaffolds to analyze the proliferative and osteolytic capability of breast cancer cells in response to varying HA nanoparticle characteristics in vitro and evaluate possible molecular mechanisms that may be involved in these changes. In Aim 3, we will correlate the physicochemical properties of HA with tumor growth and osteolytic capability in vivo and validate the contribution of specific tumor cell secreted factors as identified in aim 2. Interleukin-8 (IL-8) will be the initial focus of the proposed cytokine signaling studies, as this factor modulates metastasis-related osteolysis and tumor progression. Additionally, we will use the mineralized tumor model to identify novel factors that are regulated by nanostructural changes of HA and that may explain the molecular signature of bone-metastatic tumor cells. The novel combination of cancer biology with engineering and materials science approaches will result in a highly reproducible and pathologically relevant culture platform that will allow us to deconvolute the complexity of bone metastasis and identify molecular targets for improved therapies. By elucidating the importance of materials-based mechanisms, the proposed technology has the potential to challenge the currently accepted paradigm of bone metastasis as a disease that is solely mediated by cellular and molecular changes. Lastly, the proposed 3-D culture systems will enable radically new approaches of investigation of other physiological and pathological situations (e.g., osteoporosis, tooth regeneration) and their dependence on 3-D interactions with bone mineral. PUBLIC HEALTH RELEVANCE: Project Narrative: Bone metastasis is the leading cause of breast cancer-related deaths among women worldwide;however, the role of the bone mineral hydroxyapatite in this process remains unclear. This research will develop a three-dimensional culture platform to systematically elucidate the functional relationship between the bone mineral matrix, mammary tumor cell behavior, and metastatic osteolysis. Our studies will combine materials science with engineering and cancer biology, and this interdisciplinary approach has the potential to not only revolutionize our understanding of bone metastasis, but also provide a widely applicable culture model to study hydroxyapatite-dependent physiological and pathological processes.